1. Field of the Invention
The present invention relates to a flexible cable, and more particularly to a planar type flexible cable with shielding structure.
2. Description of the Prior Art
Connecting lines, signal cables, and flat cables are frequently used in circuit design of various electric apparatus, such as computers, measuring instruments, and control devices, so as to electrically connect among different circuit boards, circuit modules, or more than two electric apparatus to one another.
Taking the currently widely adopted notebook computer as an example, the computer is electrically connected to the liquid crystal display (LCD) screen mainly with flat connecting cables. Signal contacts at two ends of the flat connecting cable are separately connected to signal connecting terminals of the notebook computer and of the LCD screen.
In the logic circuit design for high-speed signal transmission, it is a common practice to transmit data at high speed using differential-mode signal transmission lines with shielding structure. It is possible the signal transmission lines are provided to transmit common-mode signals, in addition to the differential-mode signals. A typical differential mode signal transmission line needs an impedance value of 100 ohms, and a typical common-mode signal transmission line needs an impedance value of 100 ohms, too.
Moreover, for the flat cable to extend between two different circuit boards, circuit modules, or electric apparatus, it is conventionally required to pre-form a channel for the flat flexible cable to extend therethrough. However, in some application fields, only a round or a square channel could be formed. Such round or square channel does not allow the conventional flat cable to pass therethrough. As an alternative, the circuit designer could only use a coaxial cable to connect two different electric apparatus to each other. However, the coaxial cable does not provide a flexibility as good as the flat flexible cable. Therefore, there are many limitations in designing circuits.
It is therefore an important issue in the logic circuit for high-speed signal transmission to develop a differential-mode signal transmitting structure with good signal shielding effect, and to provide a flat layer of shielding structure that provides an impedance value needed by the differential-mode signal transmission line. And, it would be more practical to develop a planar type flexible cable with shielding structure that includes a plurality of vertically stacked insulated sections.